An alliance headed by nationalist cleric Moqtada Sadr and a rival bloc of pro-Iranian former fighters appeared to surge on Monday in surprise preliminary results from Iraq's first poll since the defeat of the Islamic State group.

Haider al-Abadi's newly created "Victory Alliance" will face the "State of Law" bloc of Nuri al-Maliki, his predecessor, key rival and Shia Dawa party co-member who now holds the post of vice president.